<!DOCTYPE html>
<head>
    <meta charset="UTF-8"/>
    <title>html5画渐变背景图片，并自动下载</title>
</head>

<body>
<center>
    <canvas id="c" width="1" height="200" ></canvas>
</center>
<script>

    //第一步：获取canvas对象
    var c = document.getElementById("c");
    //第二步：获取canvas对象的上下文对象
    var context = c.getContext("2d");

    /*
     * 这些是画其他图形代码
     context.beginPath();
     context.lineWidth=10;
     context.strokeStyle="red";
     context.moveTo(50,50);
     context.lineTo(150,50);
     context.stroke();
     context.closePath();

     //context.strokeRect(220,50,50,50);
     context.fillStyle="blue";
     context.fillRect(220,50,50,50);

     context.beginPath();
     context.arc(150,150,50,0*Math.PI/180,-180*Math.PI/180,false);
     context.lineTo(150,150);
     context.closePath();
     context.stroke();


     context.lineWidth=1;
     context.font="50px 宋体";
     context.fillText("briup",0,220);

     context.save();
     context.translate(50,50);
     context.rotate(90*Math.PI/180);

     context.beginPath();
     context.lineWidth=10;
     context.strokeStyle="red";
     context.moveTo(0,0);
     context.lineTo(100,0);
     context.stroke();
     context.closePath();

     context.restore();
     */
    var g = context.createLinearGradient(0,0,0,200);
    g.addColorStop(0,"90BFFF");
    g.addColorStop(1,"white");
    context.fillStyle = g;
    context.fillRect(0,0,1,200);

    window.location = c.toDataURL("image/jpeg").replace("image/jpeg","image/octet-stream");
</script>

</body>